The Libyan government condemned the heavy fighting between rival militias that broke out early Sunday around Tripoli's airport that killed at least six and injured 25.

Explosions and anti-aircraft gunfire were heard on the airport road from the early morning until the late afternoon.

Residents said that militiamen from the northwestern region of Zintan who had controlled the airport came under fire, and local TV footage suggested that the attacking rebels were from the western city of Misrata.

In this image made from video by The Associated Press, smoke rises from the direction of Tripoli airport in Tripoli, Libya, July 13, 2014.

A spokesman for Prime Minister Abdullah al-Thinni read a statement denouncing the attacks.

“These forces are exercising without any orders, or legitimate cover (from the government), and from multiple locations, are bombarding and conducting military operations that threaten everyone,” Ahmed Lamin said at a news conference.

Airport closed for days

Civil aviation authorities announced the airport will be closed for at least three days because of security concerns.

"The government is demanding that the attackers unconditionally and immediately stop military action," Lamin said. "We hold the leaders of these groups fully responsible legally for the use of weapons, shedding the blood of the people, especially in the holy month of Ramadan."

The fighting is part of growing turmoil in the North African oil producer, where the government is unable to control battle-hardened militias that helped to overthrow Moammar Gadhafi in 2011, but continue to defy state authority.

The Operations Cell of Libyan Revolutionaries, a coalition of Islamist militias, claimed responsibility.

The opposing groups are seen as the armed wings of two political factions, the liberals and Islamists, struggling for the upper hand in the Libyan parliament.

The statement said the government was seeking to contain the fighting.

“The government has given orders to both the ministry of interior and the army to secure the capital's streets and neighborhoods, as well as vital locations and installations. The government has also declared a state-of-emergency within all hospitals and healthcare facilities,” Lamin said.

The assault on the Zintan militia came after the United Nations pulled staff from Libya, citing security reasons, and as Washington warned of further escalation.

An airport official said rockets struck the airport perimeter around 6 a.m. (0400 GMT), followed by heavy clashes between the gunmen.

The clashes later scaled down to intermittent exchanges of automatic weapons fire, said a correspondent for the French news agency AFP.

Nabaa TV showed a Libyan Airlines plane and a transport aircraft engulfed in smoke while vehicles fired anti-aircraft volleys and fighters took up positions next to a field of sheep.

Libyan official can't travel

The closure prevented Libya's foreign minister, Mohamed Abdelaziz, from travelling to a two-day meeting near Tunis opening Sunday of his counterparts in North Africa to consider how to aid chaos-riddled Libya.

A foreign ministry source said Libya would be represented by its ambassador to Tunisia, Mohamed al-Maalul, at the closed-door meetings in Hammamet, a town south of Tunisia's capital.

Sunday's fighting was the worst in the capital since more than 40 people were killed in clashes between militias and armed residents in November.

The violence comes as the country awaits the results of the June 25 parliamentary elections.

Officials and Libya's partners had hoped the vote would give a push to state building and ease political tensions.

On Saturday, U.S. State Department spokeswoman Jen Psaki said in a statement the U.S. is "deeply concerned" the ongoing violence in Libya could lead to "widespread conflict."

Psaki stressed the importance of Libya's Constitutional Drafting Assembling in "building the country for which Libyans sacrificed so much during the revolution."

The new constitution has been billed as a milestone in the North African country's transition from Gadhafi dictatorship.